Republicans may fight to keep one part of Obamacare

One of the Obama administration's main strategies to reduce the number of uninsured Americans was to expand Medicaid — the federal health insurance program for the poorest U.S. citizens.

Top 2016 issues: Health, Obamacare opinions, Medicare, Abortion

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2016 issues: Health, Obamacare opinions, Medicare, Abortion

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2016 issues: Health, Obamacare opinions, Medicare, Abortion

MANHATTAN, NEW YORK CITY, UNITED STATES - 2015/08/22: Assembly of some 150 anti-abortion protesters behind barricade in front of Planned Parenthood. A coalition of anti-abortion protesters protested on Mott Street in Manhattan in front of Planned Parenthood. (Photo by Andy Katz/Pacific Press/LightRocket via Getty Images)

MANHATTAN, NEW YORK CITY, UNITED STATES - 2015/08/22: Protester with Baby Doe sign in front of Planned Parenthood. A coalition of anti-abortion protesters protested on Mott Street in Manhattan in front of Planned Parenthood. (Photo by Andy Katz/Pacific Press/LightRocket via Getty Images)

WASHINGTON, DC - JULY 28: Republican presidential candidate Dr. Ben Carson speaks at a anti-abortion rally opposing federal funding for Planned Parenthood in front of the U.S. Capitol July 28, 2015 in Washington, DC. Planned Parenthood faces mounting criticism amid the release of videos by a pro-life group and demands to vote in the Senate to stop funding. (Photo by Olivier Douliery/Getty Images)

WASHINGTON, DC - JULY 28: Republican presidential candidate, U.S. Sen. Ted Cruz (R-TX) speaks during a Anti-abortion rally opposing federal funding for Planned Parenthood in front of the U.S. Capitol July 28, 2015 in Washington, DC. Planned Parenthood faces mounting criticism amid the release of videos by a pro-life group and demands to vote in the Senate to stop funding. (Photo by Olivier Douliery/Getty Images)

UNITED STATES - JANUARY 22: Pro-choice protesters chant in front of the Supreme Court on Thursday, Jan. 22, 2015, the anniversary of the Roe v Wade abortion decision. (Photo By Bill Clark/CQ Roll Call)

UNITED STATES - FEBRUARY 5: Sen. Marco Rubio, R-Fla., testifies during the House Oversight and Government Reform Committee hearing on 'ObamaCare: Why the Need for an Insurance Company Bailout?' on Wednesday, Feb. 5, 2014. (Photo By Bill Clark/CQ Roll Call)

UNITED STATES - JUNE 25: Affordable Care Act supporters hold up signs outside the Supreme Court as they wait for the court's decision on Obamacare on Thursday, June 25, 2015. (Photo By Bill Clark/CQ Roll Call)

UNITED STATES - JUNE 25 - Supporters of the Affordable Care Act celebrate as the opinion for health care is reported outside of the Supreme Court in Washington,Thursday June 25, 2015. The Supreme Court on Thursday upheld the nationwide tax subsidies under President Barack Obama's health care overhaul, in a ruling that preserves health insurance for millions of Americans. (Photo By Al Drago/CQ Roll Call)

RICHMOND, CA - MARCH 31: Posters about Obamacare are posted on a window during a healthcare enrollment fair at the Bay Area Rescue Mission on March 31, 2014 in Richmond, California. SEIU-United Healthcare Workers West (SEIU-UHW) held the fair to help people sign up for free and low-cost health coverage through Medi-Cal or Covered California on the final day before the sign-up deadline. (Photo by Justin Sullivan/Getty Images)

Medicaid provides health care for more than 60 million low-income Americans. It's funded by both federal and state governments.

But a Supreme Court decision in 2012 gave individual states the right to decide whether they wanted to participate in Medicaid expansion.

The law dictated that the federal government would cover the cost of expansion for the first three years in states that expanded eligibility to those earning as much as 138 percent of the federal poverty level.

When the first round of expansion began in 2014, 17 Democrat-controlled states and the District of Columbia took part. Seven Republican governors, including former GOP presidential candidates John Kasich and Chris Christie, broke party ranks to participate.

Opponents say expansion will hurt states' finances over time, since the federal government will require states to pick up 5 percent of the tab in 2017. That will rise to 10 percent in 2020.

Some experts say Republican-led states are now reluctant to repeal the expansion because it provides federally funded health care to so many.